Regarding ESXi itself, there's no need to update the host to a later 6.0 build, if you what to upgrade it to 6.5 anyway. You can do this directly.
Please remember, that in case the host is managed by vCenter Server, you'll have to upgrade vCenter Server first.
For interoperability, and upgrade paths, see VMware Product Interoperability Matrices
Ensure that your host is supported by the ESXi version/build you are going to install!
Depending on your hardware, you may need to use a vendor customized ESXi build for the upgrade!